In ITS (intelligent Transport Systems), inter-vehicle communication is carried out to transfer information between cars by using a radio wave. In the inter-vehicle communication that is carried out by using the radio wave in a predetermined band, when the number of cars that are engaged in inter-vehicle communication in a given region increases, the congestion of radio waves may occur to disable communication between the cars.
In communication between mobile phones carried out via a base station, generally, control is performed at the base station to prevent congestion. However, in the inter-vehicle communication, no base station is present to perform control for preventing congestion. Thus, when the number of cars, which are engaged in inter-vehicle communication in a given region, increases, the cars preferably perform control to prevent congestion.
Patent Literature 1 describes a vehicle communication apparatus that performs control to prevent congestion.
The vehicle communication apparatus described in Patent Literature 1 estimates a congestion state level indicating whether congestion will soon occur based on the channel utilization rate. The channel utilization rate indicates the busy rate of a channel engaged in transmission/reception.
In the vehicle communication apparatus described in Patent Literature 1, when the congestion state level is equal to or higher than a predetermined level, the transmission power of its own vehicle is set lower than that of its own vehicle when the congestion state level is lower than the predetermined level.
Thus, the vehicle communication apparatus described in Patent Literature 1 can prevent congestion by setting the transmission power low among communication parameters for its own vehicle.